Polyaxial bone anchoring device with enlarged pivot angle

ABSTRACT

A polyaxial bone anchoring device includes: an anchoring element having a shaft for anchoring in a bone and a head, the head having a spherically-shaped outer surface portion; a receiving part configured to be pivotably connected to the head, the receiving part having a top end and a bottom end, a longitudinal axis extending through the top end and the bottom end, a channel transverse to the longitudinal axis for receiving a rod, and an accommodation space for accommodating the head, the accommodation space having a lower opening at the bottom end, a sleeve-like insert piece configured to be positioned around a portion of the head and to pivot in the receiving part, the insert piece having a spherically-shaped outer surface portion, wherein a lower edge of the insert piece extends past the lower opening in a direction away from the receiving part when the insert piece is seated in the receiving part in a position in which a central axis of the insert piece is coaxial with the longitudinal axis, and wherein the insert piece has an opening with a diameter greater than or equal to a maximum diameter of the head when the head is not in contact with the insert piece; a pressure member configured to be arranged at least partially in the accommodation space, the pressure member having a lower surface portion configured to contact the head to exert pressure onto the head when the head and the pressure member are arranged in the receiving part; wherein when the head, the insert piece, and the pressure member are arranged in the receiving part, the insert piece is tiltable with respect to the longitudinal axis of the receiving part and with respect to a longitudinal axis of the anchoring element, and wherein the anchoring element and the insert piece can be locked at respective angles relative to the longitudinal axis of the receiving part by exerting pressure with the pressure member onto the head.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/304,228, filed Nov. 23, 2011, which claims priority to and thebenefit of U.S. Provisional Patent Application Ser. No. 61/417,167,filed Nov. 24, 2010, the contents of each of which are herebyincorporated by reference in their entirety, and claims priority toEuropean Patent Application EP 10 192 373.8, filed Nov. 24, 2010, thecontents of which are hereby incorporated by reference in theirentirety.

BACKGROUND Field of the Invention

The invention relates to a polyaxial bone anchoring device with anenlarged pivot angle. The bone anchoring device includes a boneanchoring element for anchoring in a bone or a vertebra, and a receivingpart for coupling the bone anchoring element to a stabilization elementsuch as a spinal rod, where the bone anchoring element is pivotable inthe receiving part and can be pivoted out of a central axis with anenlarged pivot angle. The orientation of the enlarged pivot angle may beselectable within a range of 360° around the central axis and may beautomatically achieved by pivoting the receiving part relative to thebone anchoring element.

Description of Related Art

A polyaxial bone anchoring device with an enlarged pivot angle isdescribed in U.S. Pat. No. 6,736,820. This bone anchoring deviceincludes a bone screw and a receiving part with a seat for the head ofthe bone screw. In order that the screw member can be pivoted to atleast one side by an enlarged angle, the edge bounding the free of thereceiving part is of asymmetric construction. In a modified embodiment,an insert piece is provided, which has a spherical bottom as a seat forthe head of the screw member.

US 2007/0118123 A1 describes a polyaxial bone anchor with increasedangulation. The polyaxial bone anchor has a locking element shaped andconfigured to allow an anchoring member e.g. a screw or hook topolyaxially rotate at large angles about a central axis of the boneanchor before compression locking the anchoring member within an anchorhead.

SUMMARY

Although the polyaxial bone anchoring devices described above providefor enlarged angulation in a desired orientation there is still a needfor an improved polyaxial bone anchoring device in terms of, forexample, simplicity of design.

It is an object of the invention to provide a polyaxial bone anchoringdevice that allows for adjustment of an orientation of an enlarged pivotangle, which has a simple design while also providing high efficiency offixation.

A polyaxial bone anchoring device according to embodiments of thepresent invention has few parts and is of simple design. Therefore, thebone anchoring device is easy and cost effective to manufacture. Itprovides safe fixation, since a pressure to lock an angular position ofa bone anchoring element with respect to a receiving part is appliedeffectively in an axial direction. The bone anchoring device may bedevoid of any flexible parts or portions. Therefore it is reliable, evenif during adjustment of the angular position the orientation of theenlarged pivot angle is changed several times.

A pivot angle of the bone anchoring element relative to the receivingpart is equal to or greater than 45° measured from a straight position.This renders the bone anchoring device particularly suitable for theapplication of lateral mass fixation, for example, in the cervicalspine.

The locking mechanism for locking the bone anchoring element and thesleeve-like insert piece provides for a high clamping force on a smallsurface. Therefore, the locking mechanism is efficient.

Although in a lower part of the receiving part an insert member isarranged which needs space for placement, an upper portion of thereceiving part can be designed to be small in size.

The bone anchoring device can be designed as a top loading device, wherethe bone anchoring element is inserted from the top, or a bottom loadingdevice where the bone anchoring element is inserted from the bottom.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of exemplary embodiments by means of theaccompanying drawings. In the drawings:

FIG. 1 shows a perspective exploded view of a polyaxial bone anchoringdevice with a spinal rod according to a first embodiment;

FIG. 2 shows a perspective view of the bone anchoring device of FIG. 1in an assembled state.

FIG. 3 shows a cross-sectional view of the bone anchoring device ofFIGS. 1 and 2 in the assembled state without the rod or a fixationscrew, the section being taken along a rod axis;

FIG. 4a shows a side view of a pressure element of FIG. 1;

FIG. 4b shows a cross-sectional view of the pressure element of FIG. 4a, the section being taken along line A-A in FIG. 4 a;

FIG. 4c shows a bottom view of the pressure element of FIG. 4 a;

FIG. 4d shows a perspective view of the pressure element of FIG. 4 a;

FIG. 5a shows a side view of a sleeve-like insert piece of FIG. 1;

FIG. 5b shows a perspective view of the sleeve-like insert piece of FIG.5 a;

FIG. 5c shows a cross-sectional view of the sleeve-like insert piece ofFIG. 5a along line B-B in FIG. 5 a;

FIG. 5d shows an enlarged cross-sectional view of a portion of theinsert piece shown in FIG. 5 c;

FIGS. 6a to 6e show steps of aligning a polyaxial bone anchoring deviceaccording to an exemplary embodiment, with regard to orientation of anenlarged pivot angle;

FIG. 7 shows an exploded perspective view of a polyaxial bone anchoringdevice according to a second embodiment.

FIG. 8 shows a perspective view of the bone anchoring device of FIG. 7in an assembled state;

FIG. 9a shows a cross-sectional view of the polyaxial bone anchoringdevice of FIGS. 7 and 8 in an assembled state, the section being takenperpendicular to a rod axis, wherein a bone anchoring element assumes afirst position with respect to a receiving part;

FIG. 9b shows a cross-sectional view of the bone anchoring device ofFIGS. 7 and 8 in the assembled state, wherein the bone anchoring elementassumes a second position with respect to the receiving part;

FIG. 10a shows a perspective view from below the receiving part of thebone anchoring device according to the second embodiment;

FIG. 10b shows a cross-sectional view of the receiving part of FIG. 10a, the section being taken along line C-C in FIG. 10 a;

FIG. 10c shows a side view of the receiving part of FIG. 10 a;

FIG. 10d shows a cross-sectional view of the receiving part of FIG. 10c, the section being taken along line D-D in FIG. 10 c;

FIGS. 11a to 11g show steps of assembling a sleeve-like insert piece andthe receiving part according to an exemplary embodiment;

FIG. 12 shows a perspective view of assembling a receiving part with asleeve-like insert piece and a bone anchoring element with a pressureelement according to an exemplary embodiment;

FIG. 13 shows a perspective exploded view of a polyaxial bone anchoringdevice according to a modified embodiment;

FIG. 14 shows a cross-sectional view of the polyaxial bone anchoringdevice of FIG. 13 in an assembled state;

FIG. 15 shows a perspective exploded view of a third embodiment of apolyaxial bone anchoring device;

FIG. 16 shows a cross-sectional view of the polyaxial bone anchoringdevice of FIG. 15 in an assembled state, with a rod but without afixation device, the section being taken perpendicular to a rod axis;

FIGS. 17a to 17c show different views of a pressure member of thepolyaxial bone anchoring device of FIGS. 15 and 16;

FIGS. 18a to 18b show different views of a receiving part of thepolyaxial bone anchoring device of FIGS. 15 and 16;

FIGS. 19a to 19g show steps of assembling the polyaxial bone anchoringdevice of FIGS. 15 and 16 in different views; and

FIG. 20 shows a side view of a step of use of a polyaxial bone anchoringdevice after assembly.

DETAILED DESCRIPTION

As shown in FIGS. 1 to 3, a polyaxial bone anchoring device according toa first embodiment includes a bone anchoring element 1 in the form of abone screw having a threaded shaft 2 and a head 3. The head 3 typicallyhas a spherically-shaped outer surface portion 3 a and a recess 3 b atits free end for engagement with a driver or tool. The head 3 may beheld in a receiving part 4 that couples the bone anchoring element 1 toa stabilization rod 100. In the receiving part 4, a sleeve-like insertpiece 5 providing a seat for the head 3 and a pressure member 6 forexerting pressure onto the head 3 are arranged. Furthermore, a fixationelement in the form of, for example, fixation screw 7 is provided forsecuring and fixing the rod 100 in the receiving part 4.

The receiving part 4 has a top end 4 a and a bottom end 4 b, a centralaxis C and a coaxial bore 8 extending from the top end 4 a in thedirection of the bottom end 4 b. Adjacent to the top end 4 a, asubstantially U-shaped recess 9 is provided that forms a channel forreceiving the rod 100. By means of the recess 9, two free legs areformed which are provided with an internal thread 10 for cooperatingwith the fixation screw 7.

The coaxial bore 8 opens into an accommodation space 11 provided in alower part of the receiving part 4 (e.g., nearer to the bottom end 4 b).The accommodation space 11 has a lower opening 12 at the bottom end 4 bof the receiving part 4. The accommodation space 11 further includes aseat portion 13 near the bottom end 4 b of the receiving part 4 in whichthe sleeve-like insert piece 5 may be seated. The seat portion 13 has aspherical shape, in order to provide a socket for a ball and socketjoint that is formed by the sleeve-like insert piece 5 and the receivingpart 4. It should be noted that the seat portion 13 can also be tapered,or can have various other shapes that can be used to realize a ball andsocket joint. An inner diameter of the lower opening 12 is smaller thanan inner diameter of other portions of the accommodation space 11. Itshall also be noted that an inner diameter of the coaxial bore 8 doesnot need to be constant between the top end 4 a and the accommodationspace 11. The coaxial bore 8 may have different portions with differentdiameters.

The sleeve-like insert piece 5 is shown in particular in FIGS. 3 and 5 ato 5 d. The sleeve-like insert piece 5 has an upper edge 5 a and a loweredge 5 b. Between the upper edge 5 a and the lower edge 5 b thesleeve-like insert piece 5 may have a spherically-shaped outer surfaceportion 51. A largest outer diameter of the sleeve-like insert piece isgreater than the inner diameter of the lower opening 12 of the receivingpart 4. Hence, the sleeve-like insert piece 5 cannot escape through thelower opening 12 when it is seated in the receiving part 4. Thedimension or shape of the outer spherical surface portion 51 correspondsto that of the spherically-shaped seat portion 13 in the receiving part4 in such a way that the sleeve-like insert piece 5 can pivot and rotatein the receiving part 4 when the insert piece 5 is seated in the seatportion 13. When the sleeve-like insert piece 5 rests in the seatportion 13, such that its center axis 5 c is coaxial with the centeraxis C of the receiving part 4, the lower edge 5 b projects out of thelower opening 12. When the sleeve-like insert piece 5 is pivoted orangled in the receiving part, as shown for example, in FIG. 3, at leasta portion of the lower edge 5 b still projects out of the lower opening12.

The sleeve-like insert piece 5 is hollow and has a central portion 52that is spherically-shaped with a radius corresponding to a radius ofthe spherically-shaped outer surface portion 3 a of the head 3 of thebone anchoring element 1. A lower end of the central portion 52 forms ashoulder 53. An inner diameter of the shoulder 53 is smaller than alargest outer diameter of the spherical head 3, so that the head 3 canrotate and pivot in the central spherical portion 52 of the sleeve-likeinsert piece 5, similar to a ball and socket joint. Between the shoulder53 and the lower edge 5 b, a tapered portion 54 is provided that tapersoutward to allow angulation of the bone anchoring element 1 until theshaft 2 comes into contact with the lower edge 5 b. Between thespherical central portion 52 and the upper edge 5 a, a tapered portion55 is provided which also tapers outward. An inner diameter of thetapered portion 55 and of a transition between the tapered portion 55and the spherical central portion 52 are greater than the largest outerdiameter of the head 3, so that the head 3 can be inserted from theupper edge 5 a. At an upper edge 5 a, a chamfered portion 56 is providedthat may serve as a stop for the pressure member 6.

Center points of the spherical central portion 52 and the outerspherical portion 51 may be offset in such a way that the center pointof the inner central spherical portion 52 is shifted in the directiontowards the bottom end 4 b or the lower edge 5 b, relative to the centerpoint of the outer spherical portion 51. By means of this, a range ofangulation of the bone anchoring element 1 can be further increased. Aheight of the sleeve-like insert piece 5 in axial direction is less thana height of the head 3 in an axial direction, such that when the head 3is inserted into the sleeve-like insert piece 5, a portion of thespherical outer surface 3 a of the head 3 still projects from the upperedge 5 a of the sleeve-like insert piece 5.

The pressure member 6 is shown in particular in FIGS. 1, 3, and 4 a to 4d. The pressure member 6 is substantially cylindrical with an outerdiameter that allows it to move within the coaxial bore 8 and theaccommodation space 11. The pressure member 6 has an upper end 6 a and alower edge 6 b. Adjacent its lower edge 6 b, the pressure member 6 has aspherical recess 61 with a spherical shape that matches the sphericalshape of the outer spherical surface portion 3 a of the head 3. Adjacentthe lower edge 6 b, there is a tapered portion 62 that can abut againstthe chamfered portion 56 of the sleeve-like insert piece 5. At the upperend 6 a, the pressure member 6 has a cylindrical recess 63 for receivingthe rod 100 therein. Furthermore, pressure member 6 has a coaxial bore64 for allowing access to the screw head 3 by a tool. The coaxial bore64 is also configured to allow a portion of the head 3 to extendtherethrough when the bone anchoring element is in a pivoted condition,for example, as shown in FIG. 3. A height of the pressure member 6 in anaxial direction is such that when the fixation screw 7 is tightened, thefixation screw 7 presses onto the upper end 6 a of the pressure member6, while the pressure member 6 acts onto the head 3 of the boneanchoring element 1.

The bone anchoring device according to the first embodiment may bepre-assembled in such a way that the sleeve-like insert piece 5, thehead 3 of the bone anchoring element 1 and the pressure member 6 arearranged in the receiving part 4. For assembling the bone anchoringdevice, the sleeve-like insert piece 5, the bone anchoring element 1 andthe pressure member 6 may all be inserted through the top end 4 a. Thepressure member 6 is arranged in an aligned position in which thecylindrical recess 63 is aligned with the U-shaped recess 9 of thereceiving part for receiving the rod 100. The pressure member 6 may beheld provisionally in this position, for example, by crimping.

The bone anchoring device, as a whole or in parts, is made of abio-compatible material, such as a bio-compatible metal, for exampletitanium or stainless steel, a bio-compatible alloy, such as Nitinol, orof bio-compatible plastic materials, such as, for example,polyetheretherketone (PEEK).

The steps of use, for example, for adjusting between different positionsof the bone anchoring device according to the first embodiment are shownin FIGS. 6a to 6e . First, the bone anchoring element 1 is inserted inthe bone part or in a vertebra that is to be stabilized. Usually severalbone anchoring devices are needed to fix a stabilization rod to the boneparts or vertebrae to be stabilized. After the bone anchoring elements 1are inserted, one example of which is shown in FIG. 6a , the receivingpart 4 is adjusted by pivoting and/or rotating the receiving part 4 intoa position to be able to take up or receive the stabilization rod 100.

In the conditions shown in the FIGS. 6a to 6e , the sleeve-like insertpiece 5 and the head 3 of the bone anchoring element 1 are independentlyand freely pivotable. The sleeve-like insert piece 5 is rotatable andpivotable in the receiving part 4, while the receiving part 4 and thesleeve-like insert piece 5 are rotatable and pivotable with respect tothe head 3 of the bone anchoring element 1. The sleeve-like insert piece5 provides for an enlarged range of angulation compared to boneanchoring devices where the head 3 is directly received in the receivingpart 4, because the insert piece 5 projects out of the lower opening 12,thereby enlarging or increasing a distance between the shaft 2 of thebone anchoring element 1 and the abutment provided by the edge of thelower opening 12. Since the sleeve-like insert piece 5 is rotatable andpivotable within the receiving part 4, the enlarged range of angulationcan be achieved at any position of the receiving part 4 with respect tothe bone anchoring element 1, for all 360° around the central axis C ofthe receiving part 4. As shown in FIG. 6b , pivoting of the receivingpart 4 with respect to the bone anchoring element 1 may initiallyessentially or substantially maintains a position of the sleeve-likeinsert piece 5 relative to the receiving part 4. When the shaft 2 of thebone anchoring element 1 comes into contact with the lower edge 5 b ofthe sleeve-like insert piece, as shown in FIG. 6c and in the enlargedportion according to FIG. 6d , the sleeve-like insert piece 5 is alsopivoted with the bone anchoring element 1. The shaft 2 may push theinsert piece 5 until the shaft 2 abuts against the edge of the loweropening 12 of the receiving part 4, as shown in FIG. 6e . Hence, in FIG.6e , the receiving part 4 is pivoted at a maximum pivot angle withrespect to the bone anchoring element 1. The maximum pivot angle thatcan be achieved depends on the dimensions of the sleeve-like insertpiece 5, the receiving part 4, and the bone anchoring element 1, but istypically equal to or greater than 45° measured from a straight or zeroangle position between the receiving part 4 and the bone anchoringelement 1.

While in FIGS. 6a to 6e , an example is shown in which pivoting iscarried out in a plane that contains the rod axis, it should be notedthat the same steps can be carried out at, for example, 90° to the planecontaining the rod axis, or at any other directions within 360° aroundthe central axis C of the receiving part 4.

Finally, the rod is inserted, and the inner screw 7 is tightened topress the pressure member 6 onto the head 3 to lock the head 3 and thesleeve-like insert piece 5 simultaneously.

FIGS. 7 to 12 show a second embodiment of the bone anchoring device.Parts and portions which are the same or similar to those of the firstembodiment are designated with the same reference numerals, and thedescriptions thereof are not repeated. The bone anchoring device of thesecond embodiment differs from the bone anchoring device of the firstembodiment by the construction of the receiving part and the pressuremember. All other parts may be identical or similar to those of thefirst embodiment.

The presence of the sleeve-like insert piece 5 may have the consequencethat in order to have the space for the insert piece 5, a lower portionof the receiving part may have an increased outer diameter when comparedto receiving parts which do not include such an insert piece. There is,however, a need that at a location for a rod, the receiving part has asmall or smaller size. A receiving part 4′ according to the secondembodiment may have a smaller outer diameter at an upper portion whichtakes up or receives a rod when compared to the receiving part of thefirst embodiment, as can be seen in particular in FIGS. 7, 8, and 10.The receiving part 4′ has two tapered outer surface portions 41 a, 41 bwhich taper towards the top end 4 a to reduce the size of the receivingpart 4′. The tapered outer surface portions 41 a, 41 b are located 180°offset from each other, and may be transverse to a longitudinal axis ofthe rod 100 which corresponds to a longitudinal axis of the U-shapedrecess 9. Therefore, the dimensions of the receiving part 4′ in thedirection of the rod axis is reduced compared to that of the firstembodiment. In order to have sufficient wall strength, the coaxial bore8′ may have a smaller diameter compared to the coaxial bore 8 of thefirst embodiment. The diameter of the coaxial bore 8′ may be smallerthan the largest outer diameter of the sleeve-like insert piece 5. Thecoaxial bore 8′ opens toward an accommodation space 11′. Theaccommodation space 11′ has the seat portion 13 and a lower opening 12,similarly as seen in the first embodiment. Further, the accommodationspace 11′ has a dome-shaped portion 14 between the seat portion 13 andthe coaxial bore 8′. The dome-shaped portion 14 and/or the seat portion13 define a largest inner diameter of the accommodation space 11′, whichis larger than the inner diameter of the coaxial bore 8′. Further, thereceiving part 4′ may have an outwardly tapering portion 15 taperingoutwards from the opening 12 to further increase a range of angulationof the bone anchoring element 1. The size of the accommodation space 11′is such that the sleeve-like insert piece 5 can be tilted therein whenthe insert piece 5 is introduced from the top end 4 a in a tiltedposition, as will be explained below.

In order to allow the sleeve-like insert piece 5 to be introduced fromthe top end 4 a, two opposed recesses 42 a, 42 b are provided in theinner wall of the coaxial bore 8′ and the accommodation space 11′. Therecesses 42 a, 42 b are aligned with the U-shaped recess 9. The recesses42 a, 42 b extend from a bottom of the U-shaped recess 9 into theaccommodation space 11′.

The size of the recesses 42 a, 42 b are such that the sleeve-like insertpiece 5 can be introduced from the top end 4 a in a 90° tilted position,i.e. the width of the recesses 42 a, 42 b are greater than the height ofthe sleeve-like insert piece 5 in its axial direction. The recesses 42a, 42 b extend into the accommodation space 11′ to such an extent thattilting of the insert piece 5 into the seat 13 is possible.

Furthermore, the receiving part has at least one pin hole 16 forreceiving a pin 17 as shown in FIGS. 7 to 10. The pin hole 16 may bearranged at 90° relative to the channel axis. A second pin (not shown)may be provided on, for example, an opposite side of the receiving part.However, it is not necessary to provide a second pin.

As shown in FIGS. 7, 9 a and 9 b, the pressure member 6′ differs fromthe pressure member 6 in that it has, instead of a tapered portion 62, acylindrical portion 62′ with a diameter which is slightly smaller than adiameter of a cylindrical main portion of the pressure member 6′. Theouter diameter of the lower cylindrical portion 62′ is smaller than aninner diameter of the upper tapered portion 55 of the sleeve-like insertpiece 5, so that the lower cylindrical portion 62′ can be arranged atleast partially within the upper tapered portion 55 of the sleeve-likeinsert piece 5. By means of this, the pressure member 6′ may not touchthe sleeve-like insert piece 5.

The pressure member 6′ has on one side, perpendicular to a cylinder axisof cylindrical recess 63, a coaxial recess 65 in its outer wall which isclosed towards a lower edge 6 b and open towards an upper end 6 a (see,e.g., FIG. 4a ). A bottom of the recess 65 towards the lower edge 6 bmay be rounded. The recess 65 serves for receiving the pin 17, whichholds the receiving part in an aligned position, so that the cylinderaxis of cylindrical recess 63 and a channel axis of the U-shaped recessare aligned to receive the rod 100. The recess 65 and the pin 17 form adevice or engagement for preventing rotating and escaping of thepressure member 6′ from the receiving part 4′.

The position and dimension of the pin hole 16, the pin 17, and therecess 65 may be configured such that the pressure member 6′ isprovisionally fixed to exert a slight preload onto the head 3. By meansof this the head 3 is clamped by friction before it is finally locked bytightening the fixation screw 7 and pressing down the pressure member6′. Hence, the receiving part 4′ can be held in an adjustable angularposition with respect to the bone anchoring element. Pivoting thereceiving part 4′ with respect to the bone anchoring element 1 in thisconfiguration is still possible by applying a force that is greater thanthe friction force.

The steps of assembling the bone anchoring device according to thesecond embodiment are shown with respect to FIGS. 11a to 11g . First, ascan be seen in FIGS. 11a and 11b the sleeve-like insert piece 5 istilted by 90° and inserted in the receiving part 4′ at the position ofthe U-shaped recess 9. Then, as shown in FIGS. 11c and 11d , where FIG.11d is a cross-sectional view of FIG. 11c , the insert piece 5 is moveddownward into the accommodation space 11′. Since the outer diameter ofthe insert piece 5 is larger than the inner diameter the lower opening12, the insert piece cannot escape through the lower edge of the opening12. Then, as shown in FIGS. 11e to 11g , where FIG. 11g is across-sectional view of the receiving part 4′ according to FIG. 11f ,the insert piece 5 is titled so that it is seated in the seat portion13. Thereafter, the bone anchoring element 1, which may also include thepressure member 6′ on top of head 3, is inserted from the top end 4 a.Thereafter, the pressure member 6′ is held by introducing the pin 17into the pin hole 16 until it engages the recess 65.

Use of the bone anchoring device of the second embodiment is similar tothat of the first embodiment.

FIGS. 13 and 14 show a modification of the second embodiment. All partswhich are identical or similar to those of the second embodiment aredesignated with the same reference numerals, and the descriptionsthereof are not repeated.

The modified second embodiment differs from the second embodiment by thedesign of the pressure member 16″ and of the fixation device 70. Thebone anchoring device has separate head and rod fixation mechanisms.This is achieved by the pressure member 6″ being taller in an axialdirection, such that, instead of the cylindrical recess 63, a U-shapedrecess 63′ is provided with legs 63 a′, 63 b′ that extend above the rod100 when the rod 100 is inserted in the channel formed by the U-shapedrecess 63′. Furthermore, the pressure member 6″ may have an oblongrecess 65′ which is closed towards both the upper end 6 a and the loweredge 6 b.

The fixation device 70 is a two-part fixation device including an innerscrew 71 cooperating with the internal thread 10 of the receiving part4′. The inner screw 71 has a coaxial threaded hole for receiving a setscrew 72. The set screw 72 acts upon the rod 100. When the inner screw71 is tightened it presses onto the top end 6 a of the pressure member6″ to exert pressure onto the head 3 of the bone anchoring element 1.With the set screw 72, the rod 100 can be fixed separately.

The assembly and use of the bone anchoring device according to themodified second embodiment is similar to that of the second embodiment.It shall be noted that similar fixation devices and modified pressuremembers can also be used in connection with the bone anchoring device ofthe first embodiment.

A third embodiment of the bone anchoring device is shown FIGS. 15 to 20.The third embodiment differs from the bone anchoring devices of theprevious embodiments in that the sleeve-like insert piece 5 can beintroduced from the bottom end 4 a of the receiving part. Therefore, thethird embodiment differs from the bone anchoring devices of the previousembodiment in that it can be categorized as a bottom loading polyaxialbone anchoring device, in which the bone anchoring element 1 can beintroduced from a bottom end 4 b. As in the previous embodiments,identical or similar features are designated by the same referencenumerals and the descriptions thereof will not be repeated.

The polyaxial bone anchoring device according to the third embodimenthas a receiving part 4″ which is sized and shaped to receive the boneanchoring element 1, the sleeve-like insert piece 5, and the pressuremember 6′″ from the bottom end 4 b. For this purpose, the receiving part4″ has at its bottom end two recesses 43 a, 43 b, which are offset by180° from each other and which may be located at positions perpendicularto the rod axis. The recesses 43 a, 43 b are open to the bottom end 4 b,and are sized and shaped such that the sleeve-like insert piece 5 can beintroduced from the bottom end 4 b into the accommodation space 11″ in a90° tilted position, for example, as shown in FIG. 19a . It should benoted that the recesses 43 a and 43 b need not necessarily be positionedat 90° with respect to the rod axis, but can be positioned also at 0° orat any other angle with respect to the rod axis. If they are located at90° with respect to the rod axis, a weakening of the overall strength ofthe receiving part may be lower. The accommodation space 11″ issubstantially hollow and hemispherical, to allow the insertion of thehead 3 with the sleeve-like insert piece and pressure member 6′″. Inother words, the accommodation space 11″ is sized and shaped so as toallow introduction and rotation of the head 3 with the sleeve-likeinsert piece 5 and pressure member 6′″ mounted thereon. A lower portionof the coaxial bore 8″ which opens into the accommodation space 11″ hasa portion 18 tapering outwards towards the bottom end 4 b. This allowsthe head 3 with mounted sleeve-like insert piece 5 and pressure member6′″ to have space to be rotated in the accommodation space 11″.

The coaxial bore 8″ can have a smaller diameter compared to the coaxialbore 8 and 8′ of the previous embodiments, since it is not necessary inthis embodiment to guide the pressure member 6′″ and/or the sleeve-likeinsert piece 5 through the coaxial bore 8″. Therefore, the size of thereceiving part 4″ in an upper area can be reduced. A diameter of thecoaxial bore 8″ as shown in FIG. 16 is smaller than the largest outerdiameter of the pressure member 6′″. Therefore, it is not necessary toprovide a provisional fixation of the pressure member 6′″ to preventescaping of the pressure member 6″′.

The sleeve-like insert piece 5 of the third embodiment is substantiallythe same as the sleeve-like insert pieces 5 of the previous embodiments.

The pressure member 6′″, as shown in FIGS. 17a to 17c , is arotationally symmetric part having an upper end 6 a and a lower edge 6b. Adjacent the lower edge 66, the pressure member 6′″ has aspherically-shaped recess 61 similarly as seen in the previousembodiments. There is no cylindrical recess for receiving the rod 100,or in other words, the upper end 6 a is a flat surface. Furthermore, thepressure member 6′″ has a coaxial bore 64 for allowing access to thehead 3 with a driver or tool, and for allowing the head 3 to extendpartially therethrough when the bone anchoring element 1 is pivoted atlarge angles. Adjacent the lower edge 6 b, an outer surface portion 62is tapered as in the first embodiment. Adjacent the upper end 6 a, thereis a small spherically-shaped outer surface portion 67 which is sizedand shaped to match with a dome-shaped portion 14′ of the accommodationspace 11′, to facilitate rotation of the head 3 with the pressureelement 6′″ mounted thereon. The portion 67 may be small, for example,the portion 67 may only be a chamfered portion to facilitate rotating.

The assembly of the third embodiment will now be explained with respectto FIGS. 19a to 19g . FIG. 19a shows a side view of the receiving part4″ and the bone anchoring element before assembly. The bone anchoringelement 1 is provided with the sleeve-like insert piece 5 and thepressure member 6′″. The sleeve-like insert piece 5 and the pressuremember 6′″ are tilted so that their central axes are perpendicular tothe central axis C of the receiving part 4″. There may be a tool forholding the bone anchoring element 1 with the sleeve-like insert piece 5and the pressure member 6′″ mounted thereon in such a position. Then, asshown in FIG. 19b , which is also a side view, the bone anchoringelement 1 with the sleeve-like insert piece 5 and the pressure member6′″ are introduced in this tilted position from the bottom end of thereceiving part 4″ through the lower opening 12 into the accommodationspace 11″. The receiving part 4″ and the tilted sleeve-like insert piece5 are oriented with respect to each other in such a manner that thesleeve-like insert piece 5 can be introduced at the position where therecesses 43 a, 43 b are provided in the receiving part 4″. FIG. 19cshows a side view along a rod axis of the position shown in FIG. 19b .FIG. 19d shows sectional view along line E-E in FIG. 19c . As can beseen in FIG. 19d upon further insertion from the bottom end, thesleeve-like insert piece 5 may extend partially into the coaxial bore 8″and the tapering portion 18 in this position.

Next, as shown in FIGS. 19e and 19f which are side views of the boneanchoring device, the sleeve-like insert piece 5 and the pressure member6″ are rotated within the accommodation space 11″ by pivoting the boneanchoring element 1. When the shaft 2 of the bone anchoring element 1abuts against a lower edge 5 b of the sleeve-like insert piece 5, thesleeve-like insert piece 5 pivots with the bone anchoring element 1.Simultaneously, the pressure member 6″ may be guided along the wall ofthe accommodation space 11″. Finally, as shown in the sectional viewaccording to FIG. 19g the sleeve-like insert piece 5 and the pressuremember 6″ are in a zero-angle position, or in other words, their centralaxes are coaxial with the central axis C of the receiving part 4″.

When the polyaxial bone anchoring device is assembled, the pressuremember 6′″ projects slightly over the bottom of the U-shaped recess 9.When the rod 100 is inserted, it touches the upper flat surface 6 a ofthe pressure member 6″′. Tightening of an inner screw 7 or anotherfixation device presses the rod 100 against the pressure member 6′″,which in turn presses onto the head 3 of the bone anchoring device, tosimultaneously lock the angular position of the head 3 within thesleeve-like insert piece 5 and of the sleeve-like insert piece 5 withinthe receiving part 4″.

Further modifications of the embodiments described may also be made. Forexample, for the bone anchoring element, various different kinds ofanchoring elements can be used and combined with the receiving part.These anchoring elements may be, for example, screws with differentlength, screws with different diameters, cannulated screws, screws withdifferent thread forms, nails, hooks, etc. For some anchoring elements,the head and the shaft may also be separate parts that are connectableto each other.

Other possible modifications of the receiving part may include, forexample, instead of the U-shaped recess being perpendicular to thecentral axis, a recess for the rod may be inclined, open to the side, orin the form of a closed channel. Other kinds of locking devicesincluding outer nuts, outer caps, bayonet locking devices, or others arealso possible. In some embodiments, the inner surface portion of thepressure member that contacts the head 3 may not necessarily bespherically-shaped. The inner surface portion may have any other shapethat is suitable to exert pressure onto the head.

It shall also be noted that portions of the different describedembodiments can also be combined with each other in various differentcombinations.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

1. A polyaxial bone anchoring device comprising: an anchoring elementhaving a shaft for anchoring to a bone and a head, the head comprising aspherically-shaped outer surface portion; a receiving part configured tobe pivotably connected to the head, the receiving part having a top endand a bottom end, a longitudinal axis extending through the top end andthe bottom end, a channel transverse to the longitudinal axis forreceiving a rod, and an accommodation space for accommodating the head,the accommodation space having a lower opening at the bottom end; and asleeve-like insert piece configured to pivot in the receiving part anddefining a seat configured to hold the head of the anchoring element,the insert piece having an upper end and a lower end, and comprising aspherically-shaped outer surface portion extending from the upper end tothe lower end around the entire insert piece, wherein thespherically-shaped outer surface portion of the insert piece has a firstdiameter that defines a greatest outer width of the insert piece whenthe outer surface portion of the head is held in the seat; wherein theinsert piece is insertable into the receiving part from the loweropening while the greatest outer width of the insert piece is the firstdiameter; and wherein when the head and the insert piece are held in thereceiving part and the outer surface portion of the head is held in theseat of the insert piece, the insert piece is tiltable with respect tothe longitudinal axis of the receiving part and with respect to alongitudinal axis of the anchoring element, and is rotatable withrespect to the receiving part and the anchoring element, and wherein theanchoring element and the insert piece can be locked at respectiveangles relative to the longitudinal axis of the receiving part byexerting pressure on the head.
 2. The polyaxial bone anchoring device ofclaim 1, wherein the sleeve-like insert piece and the anchoring elementare independently moveable when arranged in the receiving part and whenthe shaft of the anchoring element and the lower end of the sleeve-likeinsert piece are not in contact with one another.
 3. The polyaxial boneanchoring device of claim 1, wherein when the shaft of the anchoringelement is pivoted in a direction and engages the lower end of thesleeve-like insert piece, further pivoting of the anchoring element inthe same direction causes the insert piece to pivot together with theanchoring element.
 4. The polyaxial bone anchoring device of claim 27,wherein a lower surface portion of the pressure member configured tocontact the head is at least partially spherical.
 5. The polyaxial boneanchoring device of claim 27, wherein the pressure member is configuredto contact the head in the receiving part, and wherein when the pressuremember is in contact with the head, there is a gap between the pressuremember and the sleeve-like insert piece.
 6. The polyaxial bone anchoringdevice of claim 1, wherein the sleeve-like insert piece has aspherically-shaped inner surface portion that forms the seat for thehead.
 7. The polyaxial bone anchoring device of claim 6, whereinrespective center points of the spherically-shaped outer surface portionof the sleeve-like insert piece and the spherically-shaped inner surfaceportion of the sleeve-like insert piece are offset from each other alongthe central axis of the insert piece.
 8. The polyaxial bone anchoringdevice of claim 7, wherein the center point of the inner surface portionof the sleeve-like insert piece is closer to the lower edge of theinsert piece than the center point of the outer surface portion of thesleeve-like insert piece.
 9. The polyaxial bone anchoring device ofclaim 27, wherein the pressure member is configured to be held in thereceiving part in a position such that the pressure member exerts apreload onto the head, which clamps the head by friction before a finallocking of an angular position of the anchoring element.
 10. Thepolyaxial bone anchoring device of claim 1, wherein the sleeve-likeinsert piece is rotationally symmetrical.
 11. The polyaxial boneanchoring device of claim 1, wherein the lower opening has a circularcross section, and wherein the greatest outer width of the sleeve-likeinsert piece is larger than a diameter of the circular cross-section.12. The polyaxial bone anchoring device of claim 27, wherein when thepressure member is in the receiving part, the pressure member has apassage that opens into the accommodation space and that is configuredto accommodate at least a portion of the head when the anchoring elementis angled relative to the receiving part. 13-15. (canceled)
 16. Thepolyaxial bone anchoring device of claim 27, wherein the pressure memberhas a recess configured to receive the rod.
 17. The polyaxial boneanchoring device of claim 1, wherein the accommodation space has twodiametrically opposed recesses which extend from an edge bounding thelower opening into the accommodation space, wherein the recesses areconfigured to allow insertion of the sleeve-like insert piece from thelower opening.
 18. The polyaxial bone anchoring device of claim 17,wherein the sleeve-like insert piece is configured to be introduced intothe accommodation space from the lower opening in a tilted configurationrelative to the receiving part, and wherein the accommodation space issized and shaped to allow further tilting of the insert piece after theinsert piece is introduced into the accommodation space.
 19. A method ofcoupling a rod to a bone or vertebrae via a polyaxial bone anchoringdevice, the bone anchoring device comprising an anchoring element havinga shaft for anchoring to a bone and a head, the head comprising aspherically-shaped outer surface portion, a receiving part configured tobe pivotably connected to the head, the receiving part having a top endand a bottom end, a longitudinal axis extending through the top end andthe bottom end, a channel transverse to the longitudinal axis forreceiving a rod, and an accommodation space for accommodating the head,the accommodation space having a lower opening at the bottom end, asleeve-like insert piece configured to pivot in the receiving part anddefining a seat configured to hold the head of the anchoring element,the insert piece having an upper end and a lower end, and comprising aspherically-shaped outer surface portion extending from the upper end tothe lower end around the entire insert piece, wherein thespherically-shaped outer surface portion of the insert piece has a firstdiameter that defines a greatest outer width of the insert piece whenthe outer surface portion of the head is held in the seat, and a closureelement, wherein the insert piece is insertable into the receiving partfrom the lower opening while the greatest outer width of the insertpiece is the first diameter, wherein when the head and the insert pieceare held in the receiving part and the outer surface portion of the headis held in the seat of the insert piece, the insert piece is tiltablewith respect to the longitudinal axis of the receiving part and withrespect to a longitudinal axis of the anchoring element, and isrotatable with respect to the receiving part and the anchoring element,the method comprising: anchoring the bone anchoring device to a bone orvertebrae; tilting at least one of the receiving part or the insertpiece relative to the anchoring element; inserting a rod into thechannel; and advancing a closure element into the channel to urge therod towards the head to exert pressure on the head and to lockrespective angular positions of the insert piece and the anchoringelement relative to the receiving part.
 20. The method of claim 19,where prior to inserting the bone anchoring device into the bone orvertebrae, the method further comprises: inserting the insert piece intothe receiving part; and inserting the head of the anchoring element intothe insert piece. 21-22. (canceled)
 23. The method of claim 20, whereinthe central axis of the insert piece is offset relative to thelongitudinal axis of the receiving part when the insert piece isinserted into the receiving part.
 24. (canceled)
 25. The method of claim20, wherein the head of the anchoring element is inserted into theinsert piece before inserting the insert piece into the receiving part.26. The method of claim 25, further comprising a pressure memberconfigured to be arranged at least partially in the accommodation spaceand to exert pressure on the head when the head and the pressure memberare in the receiving part, wherein the pressure member is configured tobe arranged together with the insert piece and the head prior toinserting the insert piece into the receiving part, and the head, theinsert piece, and the pressure member are inserted into the receivingpart together.
 27. The polyaxial bone anchoring device of claim 1,further comprising a pressure member configured to be arranged at leastpartially in the accommodation space and to exert pressure on the headwhen the head and the pressure member are in the receiving part.
 28. Thepolyaxial bone anchoring device of claim 1, wherein the lower end of theinsert piece extends past the lower opening of the receiving part in adirection away from the receiving part when the insert piece is seatedin the receiving part in a position in which a central axis of theinsert piece is coaxial with the longitudinal axis of the receivingpart.
 29. A polyaxial bone anchoring device comprising: an anchoringelement having a shaft for anchoring to a bone and a head, the headcomprising a spherically-shaped outer surface portion; a receiving partconfigured to be pivotably connected to the head, the receiving parthaving a top end and a bottom end, a longitudinal axis extending throughthe top end and the bottom end, a channel transverse to the longitudinalaxis for receiving a rod, and an accommodation space for accommodatingthe head, the accommodation space having a lower opening at the bottomend; and a sleeve-like insert piece configured to pivot in the receivingpart, the insert piece comprising a spherically-shaped outer surfaceportion and defining a seat configured to hold the head of the anchoringelement, wherein the insert piece is insertable into the receiving partfrom the lower opening while the outer surface portion of the head isheld in the seat of the insert piece; wherein when the head and theinsert piece are held in the receiving part and the outer surfaceportion of the head is held in the seat of the insert piece, the insertpiece is tiltable with respect to the longitudinal axis of the receivingpart and with respect to a longitudinal axis of the anchoring element,and is rotatable with respect to the receiving part, and wherein theanchoring element and the insert piece can be locked at respectiveangles relative to the longitudinal axis of the receiving part byexerting pressure on the head.